Add m5d.8xlarge to list known shapes.
Add m5d.8xlarge to list known shapes.

PiperOrigin-RevId: 360706041

GoogleCloudPlatform/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker